Microcapsules with Distinct Dual-Layer Shells and Their Applications for the Encapsulation, Preservation, and Slow Release of Hydrophilic Small Molecules

Microcapsules with two distinct layers of shells were fabricated using an approach combining microfluidics and photopolymerization. Unlike conventional microcapsules with a single shell, a fluorinated oil layer was introduced between the lumen and the outer polymer shell. The fluorinated oil layer significantly suppresses the leakage of the encapsulated ingredients in the lumen and consequently gives the microcapsules remarkable slow release capability for hydrophilic small molecule-based payloads, such as Rhodamine 6G. The release period of Rhodamine 6G can be up to 4 months when using a photocurable resin as the shell material, and the release of Rhodamine 6G can be regulated via the osmolality of the incubation solution for porous hydrogel microcapsules. Even under maximum hypotonic conditions, the release period of Rhodamine 6G in the hydrogel microcapsules is at least 10 days. The slow release capability can be significantly enhanced (6 weeks or longer) by increasing the thicknesses of the hydrogel shell and fluorinated oil layer.